/Engine/Plugins/Animation/ControlRig/Source/ControlRig/Public/Rigs/RigHierarchy.h
Returns all Null elements
[TArray](API\Runtime\Core\Containers\TArray)< [FRigNullElement](API\Plugins\ControlRig\Rigs\FRigNullElement) * > GetNulls ( bool bTraverse ) const